Production of a reduced sulfur content and pour point high boiling gas oil



United States Patent O PRODUCTIN @F REDUCED SULFUR CONTENT This invention relates to the preparation of a highboiling hydrocarbon mixture having a satisfactory sulfur content and a low pour point and also to improved procedure for preparing residual fuels.

Heavy petroleum distillates such as heavy vacuum gas oils produced from sulfur and wax-containing crudes are frequently unsatisfactory for various applications such as industrial fuel, catalytic cracking feed stock, etc. This is due to their high sulfur content, high pour point and high viscosity. Also the residual fractions from many petroleums are unsatisfactory as low-grade or industrial fuels, or even as bunker fuel, etc., because of their high pour point, high viscosity and high sulfur content.

This invention has for its object to provide improved procedure for preparing a heavy distillate fraction having satisfactory sulfur content and pour point from a heavy vacuum gas oil, which heavy vacuum gas oil has a relatively high sulfur content and pour point. Another object is to provide improved procedure for preparing a residual fuel oil having a satisfactory sulfur content, pour point and viscosity from one -that is unsatisfactory in these properties. Other objects will appear hereinafter.

These and other objects of our invention are accomplished by subjecting a heavy vacuum gas oil having a boiling range within the range between about 650 and 1070 F. and including a substantial amount of components boiling in the range between about 750 and 1070 F. and which has an unsatisfacto-rily high sulfur content and pour point to catalytic hydrodesulfurization to remove at least about 50 percent of the sulfur contained therein. This hydrodesulfurized gas oil is then subjected to thermal cracking at a pressure between about 50 and 1200 p.s.i.g., at a temperature between about 800 and 1000 F. and at between about 2.5 and 15.0 volumes and feed per volume of furnace coil above a temperature of 750 F. per hour. The hydrodesulfurized and thermally cracked product is subjected to distillation to separate a distillate having a high pour point and wax content which is recycled to the thermal cracking step. A bottoms fraction is separated which constitutes an improved highboiling hydrocarbon mixture having a relatively low sulfur content and pour point. Our invention also includes subjecting a residual fraction having an API gravity below about 12 and a high sulfur content, pour point and viscosity to visbreaking and blending at least part of the visbroken residual fraction with the bottoms fraction produced by the hydrodesulfurization, thermal cracking and distillation operation described above.

In order to simplify the description of our invention, we will iirst refer to the accompanying drawing in which we have illustrated apparatus in which a preferred embodiment of our invention may be carried out. Referring to the drawing, numeral 2 indicates a conduit through which a crude oil containing sulfur and high melting point waxy componen-ts and yielding a heavy vacuum gas oil of unsatisfactory sulfur content and pour point is introduced into atmospheric and Vacuum distillation unit 4. In distillation unit 4 lighter fractions are separated and removed through conduit 6. A heavy vacuum gas oil or wax distillate fraction having a boiling range in the range between 650 and 1070 F. and including a substantial amount of components (at least 50 percent and preferably 60 to 90 percent) boiling between 750 and 1070 F. is separated and removed through conduit 8. The residual fraction of the crude is removed through conduit 10. The heavy vacuum gas oil fraction removed through conduit 8 will have an unsatisfactorily high sulfur content and pour point, and this distillate fraction is subjected to catalytic hydrodesulfurization in unit 12. The hydrodesulfurized product is withdrawn through conduit 14 and subjected to thermal cracking in unit 16. If desire-d small amounts of lower boiling hydrocarbons, such as gasoline, formed during hydrodesulfurization can be removed by distillation prior t-o thermal cracking.

Thermally cracked product is removed through conduit 1S and is subjected to distillation in distillation unit 20. Lower boiling materials such as gas, gasoline, and furnace oil or the like which are formed during thermal cracking are removed through conduits 21 and 22, respectively. The furnace oil from conduit 22 may be used for blending purposes if desired. A heavy wax distillate fraction having an unsatisfactory pour point is separated and recycled to the thermal cracking unit 16 through conduit 24. An undistilled fraction representing the heaviest components is removed from distillation unit 20 "via conduit 26. This material represents the nal product in accordance with the broader aspects of our invention. It has improved sulfur content and pour point A and may be employed for any purpose that a higher boiling fraction having these desirable properties is ordinarily employed. For instance, it is an excellent industrial fuel. Also it may be used as a component of a catalytic cracking feed stock.

The fraction separated in distillation unit 20 and recycled through conduit 24 is a wax distillate which has a boiling range approximately in the range of the feed stock to hydrodesulfurization unit 12. It contains a large amount of high melting point wax which was unconverted on iirst passage through the thermal cracking unit and therefore has an unsatisfactorily high pour point. It is accordingly necessary, in order to accomplish the objectives of our invention, to separate this intermediate boiling fraction and recycle it to the thermal cracking unit in order to convert these materials, which contribute undesirable properties to the iinal product, into other materials having desired properties. This recycled fraction will usually have a boiling range in the range between about 650 and 1000 F.

In accordance with a preferred embodiment of our invention the residual fraction iiowing through conduit 10 is subjected to visbreaking in visbreaking unit 2S. The visbroken residual fraction is removed through conduit 30 and is subjected to distillation in unit 32. One or more lower boiling fractions, formed during visbreaking, may be separated in distillation unit 32. Thus gasoline and furnace oil may be separated in conduits 321 and 33, respectively. This furnace oil may be used as a blending stock if desired. Also a heavy gas oil is separated and removed through conduit 34. The undistilled portion of the residual fraction is removed through conduit 36 and is blended with the hydrodesulfurized and thermally cracked fraction flowing through conduit 26- to form a heavy residual fraction having a satisfactory sulfur content, pour point and viscosity and suitable as a high-grade industrial fuel or the like.

The distillation carried out in distillation unit 32 is designed to separate lower boiling fractions, formed during visbreaking, which have a higher value than the residual fuel oil fraction. This residual fraction is removed through conduit 36 and although it is improved in properties, as compared with the feed stock to the visbreaking unit 28, it will usually be found to have an unsatisfactory sulfur content, pour point and viscosity. This is overcome by blending as described above with the distillate productor products flowing through conduit 26 (and also materials from conduits 22, 33 and 34 if desired). Thus products from conduits 26 and 22 have relatively low sulfur contents, low pour points and low viscosities. Blending with the visbroken material owing through conduit 36 in various proportions will yield a variety of products meeting a variety of specilications for a high boiling fuel oil of low sulfur content, pour point and viscosity. Also the furnace oil and gas oils flowing from conduits 33 and 34 may be used to adjust the final product to specifications if desired. Gf course, these last two streams will have a considerably higher sulfur content than the fractions flowing through conduits 22 and 26.

Th-e heavy gas oil removed through conduit 34 has a boiling range the same as or similar to that of the feed stock flowing through conduit 8. If desired it may be circulated via the conduits indicated in the drawing by dotted lines and numerals 34, 38, 40 and 42 to be mixed with the feed stock to the hydrodesulfurization unit 12 owing through conduit 8. Alternatively this heavy gas oil fraction may be mixed with the hydrodesulfurized product flowing through conduit 14 by introduction through the conduit `indicated by dotted lines and numeral 44. lf this fraction has an undesirably high sulfur content it will ordinarily be introduced into conduit 8 so that the sulfur content will be reduced in hydrodesulfurization unit 12. On the other hand, if the sulfur content of this fraction is satisfactory and the pour point is too high, it will be introduced through conduit 44 where this property is improved in thermal crack-ing unit 16. Not only will the material flowing through conduit 42 be improved in sulfur content but of course its pour point will also be improved when it flows through thermal cracking unit 16. If this expedient of introducing the fraction through conduits 42 or 44 is employed, it is advantageous to introduce about 4 to 15 percent by volume of liquid through conduits 42 or 44 based on the volume of liquid owing through conduit 8.

The feed stock to hydrodesulfurization unit 12 contains components having the boiling range specified and including substantial amounts of high melting point wax which results in an unsatisfactory pour point. The feed Stock to hydrodesulfurization unit 12 also contains sulfur compounds in excessive amounts. The sulfur content will usually be between about 1.0 percent and 4.0 percent. Asphaltic base crudes4 or mixed asphaltic-paraflin base crudes ordinarily will be used as sources of feed stock to hydrodesulfurization unit 12 as well as to Visbreaking unit Z8. When carrying out the preferred aspect of our invention in which a blended residual fuel is produced, the feed stock to hydrosulfurization unit 12, if desired, may be obtained from an entirely different crude from that used as a source of feed stock to visbreaker 28. This feed stock to visbreaker 28 may be any residual petroleum fraction comprising hydrocarbons, asphaltic materials, etc., having -a boiling range above about 1025'J F. and usually above l070 F. Such residual fractions ordinarily contain substantial amounts of asphaltic materials, wax, sulfur compounds, etc. and are frequently used as a low-grade fuel oil such as bunker fuel. However, it is generally necessary to-have a sulfur content, pour point and viscosity which meet stringent specifications and many such residual stocks a's obtained by distillation from petroleum d-o not meet these specifications. Thesefresidual feeds will ordinarily have an API gravity of less than about l2.

The hydrodesulfurization carried out in unit 12 may be any known catalytic hydrodesulfurization. Thusthe catalyst may be any hydrogenating component composited with a porous carrier such as alumina, alumina activate'd with a small amount of silica, etc. The hydrogenating component may be a Group VI and/ or Group VIII metal, metal oxide and/or metal sulfide. A particularly advantageous combination is a mixture of an iron group metal oxide and/or sulfide such as nickel and/or cobalt oxide and/or sulde with molybdenum oxide and/ or sulfide. The reaction conditions are those known for catalytic hydrodesulfurization and will ordinarily involve a temperature of between about 650 and 800 F., a hydrogen partial pressure of between about 525 and 1500 p.s.i., a space velocity of between about 0.2 and 10 volumes of feed per volume of catalyst per hour. Av hydrogen-feed stock ratio of between about 1000 and 5000 s.c.f. of hydrogen per barrel of feed will usually be employed.

The thermal cracking carried out in unit 16 may be any thermal cracking operation known in the art provided that it is relatively mild in that less than about 15 and preferably between about 10 and 15 percent gasoline is formed. The feed stock to this thermal cracking operation will ordinarily comprise l to 3 parts of recycle flowing through conduit 24 to 1 part of hydrodesulfurized product flowing from hydrodesulfurization unit 12 through conduit 14. A temperature of between about 800 and 1000 F. and a pressure of between about 50 and 1200y p.s.i.g. may be used. Between about 2.5 and 15.0 volumes of feed per volume of furnace coil above a temperature of 750 F. per hour may be used in carrying out this thermal cracking operation.

The visbreaking operation in unit 28 is of a mild type,

i.e., it is carried out in such a manner as to yield between about 5 and 13 percent gasoline and it will be found that 7 to 1l percent gasoline formation will be best with most residual stocks. We prefer to carry out the visbreaking operation to the maximum severity` which will still give a stable product, i.e., one which meets the NBTL test (Federal 3461.1) for stability. If too severe a type of visbreaking is carried out in unit 28, solids will deposit in the final visbroken product and, of course, this is undesirable. The reaction conditions employed in the Visbreaker are the same as those customarily employed for visbreaking a residual stock provided that they are selected to yield a product which is stable. The temperature during visbreaking may be between about 800 and 1000 F. and the pressure between about 50 and 300 p.s.i.g. The space velocity in volumes of feed per volume of reactor above 750 F. per hour may range between 2.5 and 15.0.

EXAMPLE per day of a crude having the inspection shown in column 1 of the accompanying table was subjected to atmospheric and vacuum distillation .and light fractions were removed in an amount of 4,940 barrels per day as indicated 4by conduit 6 `of the drawing. A heavy gas oil fraction having the inspection shown in column 2 of the table was removed via conduit 8 and introduced into catalytic hydrodesulfurization unit 12 in a'n amount of 3,040 barrels per day. A residual or bottoms fraction in an amount of 2,020 barrels per day, having the inspection shown in column 4 of the table was separated during this distillation and was introduced into visbreaking unit 28 via conduit 10.

The hydrodesulfurization in unit 12 was carried out at a hydrogen partial pressure of 623 p.s.i., at a temperature of 682 F., at a liquid hourly space velocity of 1.92 in the presence of hydrogen in the amount of 2600' s.c.f. per barrel of feed. The catalyst was nickel (2.5 percent), cobalt (1.0 percent), molybdenum (11.0 percent) deposited on activated alumina. The` hydrodesulfurized gas oil was distilled to remove 116 barrels per day of furnace oil and lighter and yield .a bottoms fraction in an amount of 2,940 barrels per day and having the properties shown 1n column 3 of the table. This bottoms fraction was to distillation in unit 32 and a gasoline stream in an amount of 115 barrels per day and having the inspection shown in column 5 of the table was removed .through blended With 222 barrels per day of heavy gas oil flo-wing Conduit 31. A furnace Ioil stream in the amount of 240 through conduits 34, 38 and 44. This heavy gas oil `stream 5 barrels per day and having the inspection shown in colof 222 .barrels per day had the properties shown in column 6 of the table was removed Ithrough conduit 33. A umn 7 of the table. This blend constituting 3,162 barrels tar bottoms fraction was removed through conduit 36 in per day had the properties shown -in column 9 o-f the an amount of 1,432 barrels per day. This tar bottoms table. To this blend was added 4,840 barrels per day of fraction had the inspection shown in column 8 of thel recycle oil owing through conduit 24. This recycle had 10 table. A heavy gas oil fraction was removed through fthe inspection shown in column 12 of the table. This conduit 34 and circulated to thermal cracking unit 16 mixture was subjected to lthermal cracking in unit 16. as described above. Y

This thermal cracking was carried out at a ytemperature A 3500 Redwood fuel having the properties shown in of 890 F. (outlet temperature), a pressure of 200 p.s.i.g., column 14 of the table was prepared by blending 832 a coil volume of 0.034 cubic foot above 750 F. per 15 barrels per day of the furnace oils from conduits 22 and barrel throughput per day and a recycle ratio of 153 33 (columns 6 and 11 of .the table) with 1,066 barrels percent. The product from thermal cracking was subper day of tar `bottoms owing through conduit 26 (coljected to distillation in unit 20. A gasoline fraction was umn 13 of the table) and with 1,432 barrels per day removed in an amount of 411 barrels per day. This oftar bottoms tlowing through conduit 36 (column 8 of gasoline had `the inspection shown in column 10 of the 20 the table). table. A furnace oil fraction was removed through con- A 350 Redwood fuel having the properties shown in duit 22 in an lamount of 1,455 rbarrels per day. This column 15 of the table was prepared by blending 1,695 furnace oil had the inspection shown in column 11 of barrels per day of furnace oils from conduits 22 and 33 the table. Also a tar bottoms fraction was removed in (columns 6 and 11 ofthe table) with 1,233 barrels per an Iamount of 1,262 barrels per day through conduit 26. 25 day of tar bottoms flowing through conduit 26 (column This tar 'bottoms fraction had the inspection shown in 13 of the table) and with 924 barrels per day of .tar column 13 of the table. bottoms owing through conduit 36 (column 8 of the The vacuum reduced crude owng through conduit 10 table). in theamount of 2,020 barrels per day had the inspection It will be evi-dent that the various product streams can shown in column 4 o f the table. This reduced crude was 30 be blended in different proportions than those specifically subjected to visbreaking in unit 28. This visbreaking mentioned, or that certain of the product streams such as operation was carried out at a temperature of 850 F. furnace oil or heavy gas oil from conduit 34 can be elimi- (outlet temperature), a pressure 2-00 p.s.i.g. and a coil nated from the blends in order `to produce different comvolume of 0.042 cubic foot above 750 F. per barrel Y binations meeting various specifications for fuels and/or throughput per day. The visbroken product was subjected to balance refinery production.

TABLE Col. No 1 2 3 4 5 6 7 8 Yield: Percent by Vol. of Crude 100.0 30.4 29.4 20. 2 1.15 2. 4 2.2 14. 3 Inspections:

Gravity: API 30. 2 22. 5 26. 5 5. 3 61.9 32. 4 17. 7 1. 4

Viscosity, SUV, sec.:

Penetration, 77 F., 100 g., 5

Fresh Point, F 675 (D92) 162(D93) Pour Point, F +10 +90 +120 -15 Sulfur, percent 1. 98 2.85 0. 65 5.17 0. 99 2. 52 6. 0 Nitrogen, pereent 0.082 0.068 0.5 Sediment by Extraction,

percent 0. O1 0.02 Carbon Residue, Ramsbottorn, percent 0. 50 0.10 21. 7 Carbon Residue, Conradson, percent 34.1 Insoluble in n-Pentane, percent 18.6 Aniline Point, "F 145 Octane Number, Adjusted to 10 RVP;

3 hr- 1 Heating Value, Gross,

B.t.u./1b 17, 175 Hydrogen, percent 8, 7 Heating Value, Net, B.t.u./

1b...- 16, 380 Thermal Stability Distillation, F.:

Over Point 115 una 330 693 167 767 204 829 230 901 266 09o 297 TABLE-Continued Col. No 10 Yield: Percent by Vol. of Crude Inspections:

Gravity: API ViseosityI,` S UV, sec.: v

F Softening Point,

3,500 (Redwood)- 350 (Redwood).

F Penetration, 77 F., 100 g., 5 sec...

Flash Point, F Pour Point, F Sulfur, percent Nitrogen, percent Sediment by Extraction, percent- Carbon Residue, Ramsbottom,

percent Carbon Residue, Conradson, percent..

Insolubl-ein n-Pentane, percent.. Aniline Point, F Oetangy Number, Adjusted to 10 Motor, Clear Motor, +2 ce. TEL

Research, Clear Research, +2 ce. TEL

Copper Strip Test, 122 F., 3 hr Copper Strip Test, 212 F., 3 hr.-. Heating Value, Gross, B.t.u./lb Hydrogen, percent Heating Value, Net, Btu/lb. Thermal Stability Distillation, F.'

Over Point We claim:

1. The process for reducing the sulfur content and pour point of a heavy vacuum gas oil having a boiling range within the range between about 650 and 1070 F. and

including a substantial'amount of components boiling inY hydrodes-ulfurized gas oil to thermal cracking to form less A than about 15 percent gasoline, subjecting the product from the thermal cracking to distillation to separate an intermediate distillate boiling above about 650 F. and having a high pour point and wax content, recycling this distillate to the thermal cracking step and separating a bottoms fraction constituting an. improved high-boiling hydrocarbon mixture having a relatively low sulfur content and pour point.

2. The process for reducing the sulfur content and pour point of a heavy vacuum gas oil having a boiling range within the range between about 650 and 1070 F. and including a substantial amount of components boiling in the range between about 750 and 1070 F., which process comprises subjecting said heavy vacuum gas oil to catalytic hydrodesulturization at a temperature between about 650 and 800 F., at a hydrogen partial pressure between about 525 and 1500 p.s.i., at a space velocity between about 0.2 and 10, whereby at least 50 percent of the sulfur compounds are converted into hydrogen suliide, subjecting the hydrodesulfurized gas oil to thermal cracking at a pressure between about 50 and 1200 p.s.i.g., at a temperature between about 800 and 1000 F. and at a space velocity between about 2.5 and 15.0v to form between about 10 and 15 percent gasoline, subjecting the product from the thermal cracking to distillation to separate a distillate having a high pour point and wax content, and 4having a boiling range in the range between about 650 and 1000 F., recycling this distillate to the thermal cracking step in amount of,1 to 3 Volumes to one of fresh feed to the thermal cracking step and separating a heavier bottoms fraction constituting an improved high-boiling hydrocarbon mixture having a relatively low sulfur content and pour point.

3. The process for reducing the sulfur content and pour point of a heavy gas oil having a boiling range within the range between about 650 and 1070 F. and including a substantial amount of components boiling in the range between about 750 and 1070 F., which process cornprises subjecting said gas oil to catalytic hydrodesulfurization at a temperature between about 650 and 800 F., at a hydrogen partial pressure between about 525 and 1500 p.s.i., at a space velocity between about 0.2 and 10, whereby at least 50 percent ot the sulfur compounds are converted into hydrogen sulfide, subjecting the hydrodesulfui-ized gas oil to thermal cracking at a pressure between about 50 and 1200 p.s.i.g., at a temperature between about 800 and 1000" F. and at a space velocity between about 2.5 and 15.0 to form between about 10 and 15 percent gasoline, subjecting the product from the thermal cracking to distillation to separate an intermediate distillate boiling above about 650 F. and having a high pour point and wax content, recycling this distillate to the thermal cracking step, separating a bottoms fraction constituting an improved high-boiling hydrocarbon mixture having a relatively low sulfur content and pour point, subjecting a vacuum reduced crude having a gravity below about 12 A.P.I. to visbreaking and blending at least a portion of the visbroken residue with said improved high-boiling hydrocarbon mixture to produce a blend having a lower sulfur content, pour point and viscosity than the vacuum reduced crude.

4. The process 4for reducing the sulfur content and pour point of a heavy gas oil having a boiling range within the range between about 650 and 1070 F. and including a substantial amount of components boiling in the range between about 750 and 1070 F., which process cornprises subjecting said gas oil to catalytic hydrodesulfurization at a temperature between about 650 and 800 F., at a hydrogen partial pressure between about 525 and 1500 p.s.i., at a space velocity between about' 0.2 and 10, whereby at least 50 percent of the sulfur compounds are converted into hydrogen sulfide, subjecting the hydrodesulfurized gas oil to thermal cracking at a pressure between about 50 and 1200 p.s.i.g., at a temperature between about 800 and 1000 F. and at a space velocity between -about 2.5 and 15 .0 to form between about 10 and 15 percent gasoline, subjecting the product from the thermal cracking to distillation to separate an intermediate distillate boiling above about 650 F. and having a high pour point and wax content, recycling this distillate to the thermal cracking step, separating a bottoms fraction constituting an improved high-boiling hydrocarbon mixture having a relatively low sulfur content and pour point, subjecting a vacuum reduced crude having a gravity below about 12 A.P.I. to visbreaking, distilling the visbroken material to obtain a heavy gas oil fraction and a bottoms fraction, adding at least part of this heavy gas oil fraction to the feed stock flowing to a member of the Vgroup consisting of the hydrodesulfurization and thermal cracking steps and blending at least a portion of the visbrolgen bottoms fraction with said improved high-boiling hydrocarbon mixture to produce a blend having a lower sulfur content, pour point and viscosity than the vacuum reduced crude.

5. The process of claim 4 wherein the high pour point 10 and wax content distillate separated from the thermally cracked product boils in the range from about 650 to about 1000" F., the vacuum reduced crude boils above about 1070 F. and the heavy gas oil fraction distilled from the visbroken material boils in the range from about 650 to about 1070 F.

References Cited by the Examiner UNITED STATES PATENTS 1,932,174 10/1933 Gaus et al 20'8-89 2,132,137 10/1938 Watson 20S-80 2,906,694 9/ 1959 Dunlap et al 208-79 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

A. RIMENS, Assistant Examiner. 

1. THE PROCESS FOR REDUCING THE SULFUR CONTENT AND POUR POINT OF A HEAVY VACUUM GAS OIL HAVING A BOILING RANGE WITHIN THE RANGE BETWEEN ABOUT 650* AND 1070*F. AND INCLUDING A SUBSTANTIAL AMOUNT OF COMPONENTS BOILING IN THE RANGE BETWEEN ABOUT 750* AND 1070*F., WHICH PROCESS COMPRISES SUBJECTING SAID HEAVY VACUUM GAS OIL TO CATALYTIC HYDRODESULFURIZATION TO REMOVE ABOVE ABOUT 50 PERCENT OF THE SULFUR CONTAINED THEREIN, SUBJECTING THE HYDRODESULFURIZED GAS OIL TO THERMAL CRACKING TO FORM LESS THAN ABOUT 15 PERCENT GASOLINE, SUBJECTING THE PRODUCT FROM THE THERMAL CRACKING TO DISTILLATION TO SEPARATE AN INTERMEDIATE DISTILLATE BOILING ABOVE ABOUT 650*F. AND HAVING A HIGH POUR POINT AND WAX CONTENT, RECYCLING THIS DISTILLATE TO THE THERMAL CRACKING STEP AND SEPARATING A BOTTOMS FRACTION CONSTITUTING AN IMPROVED HIGH-BOILING HYDROCARBON MIXTURE HAVING A RELATIVELY LOW SULFUR CONTENT AND POUR POINT. 